Conventionally, in the medical and drug discovery fields, and the like, cells, etc., that are cultured in a sample container called a “well plate”, a “microplate”, etc., are observed as samples. A plurality of concave sample storage portions called wells are formed in such a sample container. In general, samples are filled in the wells together with liquid medium. In recent years, image capturing of such samples by an imaging device having a CCD camera, etc., mounted thereon and observation of the samples using image data obtained by the image capturing have been performed. For example, in cancer drug discovery research, by capturing, by the imaging device, images of cancer cells filled in the wells together with a liquid (culture fluid) serving as medium, observation and analysis of the cancer cells are performed.
FIG. 23 is a perspective view showing an example of a well plate 20. In the example shown in FIGS. 23, 24 wells 21 are provided in the well plate 20. When image capturing by an imaging device is performed, such a well plate 20 is placed (set) in a predetermined position on a stage by an operator. More specifically, a holder 121 for holding the well plate 20 is formed in a stage 12, for example, as shown in FIG. 24, and the well plate 20 is placed in the holder 121 by the operator.
Meanwhile, normally, the operator places the well plate 20 such that a corner of the well plate 20 matches a corner of the holder 121 as shown in a portion indicated by reference character 90 in FIG. 25. By this, the well plate 20 is held in the holder 121 in an ideal state, and a desired captured image can be obtained. However, for example, when the operator roughly places the well plate 20 or when some kind of external force is applied to the well plate 20 before starting image capturing, the well plate 20 may not be held in the holder 121 in the ideal state upon the start of image capturing. For example, as shown in FIG. 26, upon the start of image capturing, the well plate 20 may be placed in an obliquely dislocated state from the ideal state (a turned state from the ideal state). If image capturing is performed in such a state in which positional displacement has occurred, a desired captured image cannot be obtained, e.g., an image of a range different than a desired range is obtained.
For a technique that deals with positional displacement such as that described above, for example, there is known a technique using pattern matching (hereinafter, referred to as “first conventional technique”). In the first conventional technique, an actual center position of a well is found by performing pattern matching, such as normalized correlation, using a captured image obtained in a state in which positional displacement has occurred, and a pre-registered template image. In addition, according to a technique disclosed in Japanese Laid-Open Patent Publication No. H10-27246 (hereinafter, referred to as “second conventional technique”), the centers of gravity of feature locations in binarized images which are obtained by binarizing a captured image and a template image are found, and an angle and the amount of parallel displacement between the captured image and the template image are found based on regression lines which are obtained from the respective arrangements of the centers of gravity.